Streamplot examples for adding scatter plot data to graph does not work

[jonmmease]

Originally reported by @TakodaS in https://github.com/plotly/plotly.py/issues/1555

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The streamline and source point example given does not work because the line fig['data'].append(source_point) throws an error message saying you can't append to a tuple. I There is an easy workaround:

new_data = [*fig['data'],source_point]
py.iplot(new_data, filename='streamline_source')

But as of now you are not able to append new data to an existing figure, which makes the example shown and the example in the create_streamline docstring fail to compile and I think this should be fixed.